1. Field of the Invention
The invention relates to a LCD (Liquid Crystal Display) and a driving method therefor, and more particularly to a LCD with improved motion image quality and a driving method therefor.
2. Description of the Related Art
A conventional cathode ray tube (CRT) monitor displays a frame in an impulse type manner, and each pixel in each frame time emits light only for an instant. FIG. 1 shows a relationship between the brightness and the time in a pixel of a cathode ray tube monitor. Pixel data D1, D2 and D3 enable the pixel to generate the corresponding brightnesses I1, I2 and I3 in frame times T1, T2 and T3. Because the impulse type CRT monitor has a quick response speed, the frame that is currently displayed is free from being influenced by the brightness of a previous frame, and no image retention occurs in the motion image.
The conventional LCD displays images in a hold type manner, and the brightness of the pixel thereof is kept constant in a frame time. FIG. 2 shows a relationship between the brightness and the time in a pixel of a conventional LCD (Liquid Crystal Display). The pixel generates different brightness curves L1, L2 and L3 in the frame times T1′, T2′ and T3′ according to different driving voltages V1, V2 and V3. As shown in FIG. 2, because the response speed of the liquid crystal molecule is smaller than the changing speed of the electric field, a period of response time is needed for the pixel to reach the target brightness. As clearly illustrated in the brightness curve L2 of FIG. 2, the brightness L2 does not reach the brightness, which should correspond to the driving voltage V2, until the frame time T2′ almost elapses.
Because the response speed of the liquid crystal molecule is not high enough, retained images tend to occur when the LCD is displaying the motion images and thus influence the display quality. In the hatched area of FIG. 2, for example, because the displayed image in the frame time T2′ is stilled retained at the beginning of the frame time T3′, the retained image overlaps with the to-be-displayed image in the frame time T3′, and the motion image quality of the LCD is thus influenced.